Robot Watch

The easiest way to send a robot to another planet is to make it small, so it can fly on a cheap rocket. But an ideal explorer should be big, so that it is stable. That conundrum drove mechanical engineer Shigeo Hirose and his colleagues at the Tokyo Institute of Technology and the National Space Development Agency of Japan to build Tri-Star II. Tri-Star II has folding legs and three collapsible wheels that consist of loops of overlapping metal plates. When the robot is deployed, battery-powered motors in each hub unwind the loops, doubling their size. Once enlarged, the wheels can clamber over rocks and out of ditches that would stymie a smaller vehicle. The springy wheels minimize vibrations to sensitive machines mounted on the rover. And each wheel can move independently in any direction.